Mesh text individual letters change colors
Speaking from Vers 2.77 here but 2.8+ should be the same or very similar...
Once you've changed your text to mesh you should be able to do that at least two ways -
1:
In edit mode select only those faces on the word(s) you wish to re-colour.
Assign them a new material slot and change it's colour.
2:
In edit mode, select the vertices in only the word(s) you wish to re-colour,
Part them from the mesh with &quot;P&quot;.
Return to Object mode and select the words as a separate mesh and give it a new material slot if it hasn't got one already.  Colour it as required.
Parent the new mesh to the main text body if it's to be moved.
Colours can be changed with keyframes as with any other animation.